The compounds of the invention referred herein, are pharmaceutically acceptable salts of the compound known by its generic name Clopidogrel having structure (I)

It is available in the market as its bisulfate salt and is marketed by Sanofi-Synthelabo as “Plavix” having the general formula (II)

Clopidogrel is an inhibitor of platelet aggregation and is marketed as an antianginal agent, antiplatelet agent and is found to decrease morbid events in people with established atherosclerotic cardiovascular disease and cerebrovascular diseases.
The therapeutic application of Clopidogrel as blood-platelet aggregation inhibiting agents and antithrombotic agent and its preparation is disclosed in U.S. Pat. No. 4,529,596. U.S. Pat. No. 4,847,265 describes the process for the preparation of the hydrogen sulfate salt of Clopidogrel.
Polymorphs of Clopidogrel bisulfate has been described in U.S. Pat. Nos. 6,504,040 and 6,429,210. We have disclosed novel polymorphs of Clopidogrel bisulfate in our PCT International Application No. PCT/IN03/00053.
The present applicant has also disclosed novel processes for preparing Clopidogrel base in U.S. Pat. No. 6,635,763.
U.S. Pat. No. 4,847,265 discloses that the dextrorotatory enantiomer of formula (I) of Clopidogrel has an excellent antiagregant platelet activity, whereas the corresponding levorotatory enantiomer of Formula (I) is less tolerated of the two enantiomers and is less active. U.S. Pat. No. 4,847,265 also describes various other salts of the compound of formula (I), like its hydrochloride, carboxylic acid and sulfonic acids salts. Specifically, salts of acetic, benzoic, fumaric, maleic, citric, tartaric, gentisic, methanesulfonic, ethanesulfonic, benzenesulfonic and, lauryl sulfonic acids were prepared. However, according to this patent, these salts usually precipitated in amorphous form and/or they were hygroscopic making them difficult to handle in an industrial scale. Also, no data corresponding to any of these salts are reported. The specification also describes salts of dobesilic acid (m.p.=70° C.) and para-toluenesulfonic acid, having a melting point of 51° C., the purification of which, as accepted in the patent, proved to be difficult.
Thus, there remains a need to prepare salts of Clopidogrel which are stable, easy to handle, can be purified and can be exploited on an industrial scale.
We hereby disclose certain pharmaceutically acceptable salts of Clopidogrel particularly the salts of p-toluenesulfonic acid, benzenesulfonic acid and methanesulfonic acids both in crystalline and amorphous forms, including their hydrates and other solvates which are well characterized, free flowing, easy to handle and having high purity.